Any idea on how to desolder a shorted mosfet?

[JorgeHernan]

Hello.I have tried with my 30 watts soldering iron but it is impossible.Thanks

[gdement]

Re: Any idea on how to desolder a shorted mosfet?

I've only done this a couple times. They can be pretty difficult, not sure if the 30W will be able to do it. It definitely needs to be clean and running at it's best. Use a flat chisel tip - a pointed tip won't work.

Get a small tool to help you lift the legs while you melt them with the iron. Clear any trailing solder so the legs are free. When legs are free you can retest to make sure the mosfet is actually shorted. I'm assuming you may have already gotten to this point.

Remove any components blocking the tab at the back. Make sure the edge on your tip is clean.
Put flux on the tab, and put the iron up against the point where the tab meets the board. It might help to move the tip around the edge of the tab some, rather than heating only one spot. You may be able to see solder on the edge of the tab starting to melt. At that point you just need to give it more time to finish melting. I use some moderate pressure and eventually the mosfet will let go. If you're lucky it won't go flying across the room.

It takes a lot of heat to get the solder underneath the tab to melt. I wasn't able to do this on my 25W iron, but my 40W can do eventually do it. If you buy an iron for this purpose then a hotter one is more desirable.

[Topcat]

Re: Any idea on how to desolder a shorted mosfet?

Easiest way is with a SMT soldering station, they come right off.

[starfury1]

Re: Any idea on how to desolder a shorted mosfet?

To add to the Above

If the fet is truly stuffed you could just cut the legs at the body with "nippy cutters"
(being careful not to cut into the pcb in anyway)
you then hold the legs with needle nose pliers or long tweezes

let you tip heat up and just add a small amount of solder to get better heat transfer
heat up pad and remove legs

The body is going to be harder and yeah the hotter the iron the better.
It really depends on how well your iron get maintain and dump heat
(so as above)

You need to hold hold the body, again add a bit of solder to the tip get better heat transfer.

once it gets nice and hot solder will melt just lift it off

clean up the pads with solder wick and liquid flux as needed

we can only give you pointers the skill is up to you...yes a hotter is better so you may need to get another iron

If you can, find some junk boards to practice on first..... it would be a good idea

But there is nothing like have the right tool for the job...trouble is $$$$ not that cheap

something like these here
would do

Lastly
Dumping too much heat for too long a time, you stand a chance of causing damage.
So just don't over do it....which is Why I recommend junk pcb first till you get a feel for it
If your iron don't cut it get another iron

HTH

Cheers

[gonzo0815]

Re: Any idea on how to desolder a shorted mosfet?

Just get a high power iron, even the cheapest will do for it.
I personally have always used my big & cheap 80w iron, and it wennt smoth and fast.

Ok, i know that there could be some problems with ESD, induced voltage etc. with cheap irons.
But if you do not want to become a elektronik expert, spending a couple hundred of dollars for good equipment this is the better choice, than destroying your board due to inadequat iron.

Any way, it would not hurt to short the whole bord and limiting the ESD problems.
You can either use a antistatic foil or some aluminia foil and place the board on it.
But i would not ground it.

[Maxxarcade]

Re: Any idea on how to desolder a shorted mosfet?

Any way, it would not hurt to short the whole bord and limiting the ESD problems.
You can either use a antistatic foil or some aluminia foil and place the board on it.
But i would not ground it.

If doing this, please remove the CMOS battery first

[JorgeHernan]

Re: Any idea on how to desolder a shorted mosfet?

some of my friends recommended a heat gun among other things.If i get to desolder somehow that mosfet then comes the next problem : find a good same package mosfet.There are no transistors of that types available so i will have to find another dead motherboard that comes with the same mosfets.

[Logistics]

Re: Any idea on how to desolder a shorted mosfet?

For a long time, I didn't know that you aren't supposed to sand your tips to get the old junk off; that they had some sort of coating on them. So I always took a piece of 120 or so and sanded my tips down to the copper or whatever they are. This always seemed to make the tip just want to cut through solder with a quickness. If you have a tip you don't mind ruining... or sanding before every use like I did ^_^ just sand it down till the coating is gone and see if it eats through that solder then.

[gonzo0815]

Re: Any idea on how to desolder a shorted mosfet?

I would do this only with not iron coated or long life tips.
I would suggest Tippy tip cleaner, it is probably mixture of thin and ammonium chloride.
It is working very good, especially if you have to solder with higher temps.

Heat gun is not the ideal tool for that kind of work. You will probably harm the board.

[byteexp]

Re: Any idea on how to desolder a shorted mosfet?

sir how do i test for shorted vrm/fets? thanks